Fast HR-EBSD Based Pattern Center Calibration

High fidelity pattern center calibration is critical for resolving pseudo symmetry in difference phases, maximizing indexing precision, and extracting accurate strains from HR-EBSD calculations [1]. Camera displacement, band error, and forward model approaches all have shortcomings [2]. Shadow casting approaches can be effective but require dedicated hardware [3]. HR-EBSD can be used to calibrate pattern centers by removing phantom strain [4]. This approach produces excellent results with suitable pattern selection, but requires iterating a loop that includes both reference pattern simulation and HR-EBSD alignment. The homography approach to HR-EBSD is a full field approach that computes the warp to align moving patterns to a reference pattern [5]. An analytic expression bidirectionally converts between homography matrix and F tensor using the pattern center [5]. By combining both approaches pattern simulation and HR-EBSD alignment are moved outside the calibration loop. With an analytic pattern center update formalism the iteration speed is significantly improved enabling rapid high quality pattern center calibration as shown in figure 1. An example pattern center calibration result for Titanium showing an experimental pattern (left), a simulated pattern using the calibrated orientation and pattern center (center) and the difference between them (right).